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| United States Patent |
5,210,345
|
|
Mielke
|
May 11, 1993
|
Process for the preparation of vinyl chloride
Abstract
An addition of benzotrichloride produces a significantly higher yield of
vinyl chloride in the thermal cleavage of 1,2-dichloroethane.
| Inventors:
|
Mielke; Ingolf (Burgkirchen, DE)
|
| Assignee:
|
Hoechst Aktiengesellschaft (Frankfurt am Main, DE)
|
| Appl. No.:
|
959040 |
| Filed:
|
October 9, 1992 |
Foreign Application Priority Data
| Current U.S. Class: |
570/227; 570/226 |
| Intern'l Class: |
C07C 017/34 |
| Field of Search: |
570/227,226
|
References Cited
U.S. Patent Documents
| 4851597 | Jul., 1989 | Felix et al.
| |
Primary Examiner: Mars; Howard T.
Attorney, Agent or Firm: Connolly and Hutz
Claims
I claim:
1. A process for preparing vinyl chloride, comprising: thermally cleaving
1,2-dichloroethane in the presence of benzotrichloride.
2. The process as claimed in claim 1, wherein the thermal cleavage is
performed at 300.degree. to 600.degree. C. at a pressure from atmospheric
pressure to 50 bar.
3. The process as claimed in claim 1, wherein at least 250 ppm of
benzotrichloride are added to the 1,2-dichloroethane.
4. The process as claimed in claim 2, wherein at least 250 ppm of
benzotrichloride are added to the 1,2-dichloroethane.
Description
DESCRIPTION
U.S. Pat. No. 4,851,597 discloses carrying out the thermal cleavage of
1,2-dichloroethane (EDC) to give vinyl chloride (VC) in the presence of
trichloroacetyl chloride or a compound having 3 carbon atoms, at least 6
chlorine atoms, 0 or 1 oxygen atom and, per carbon atom bound to this, 0
or 1 hydrogen atom. As a result of these additions, the degree of
conversion is increased or, at the same conversion, the cleavage
temperature is reduced, as a result of which a reduction of by-products is
observed.
Surprisingly, it has now been found that in this reaction, an addition of
benzotrichloride effects a still substantially greater increase in
conversion. The invention therefore relates to the use of benzotrichloride
as an additive in the thermal cleavage of EDC to give VC.
The reaction can be carried out according to the details of U.S. Pat. No. 4
851 597. Preferred embodiments of the invention are described in more
detail below:
The thermal cleavage is expediently carried out at 300 to 600.degree. C.,
at atmospheric pressure or elevated pressure up to about 50 bar (5 MPa).
Preference is given to pressures from 10 to 40 bar (1 to 4 MPa).
Even relatively small amounts of benzotrichloride produce significantly
increased conversions to VC. Thus, for example, 250 ppm of
benzotrichloride increase the VC yield from about 52% (feed EDC without
additive) to about 76%. Higher levels of addition cause a further, but not
so great, increase in yield.
Surprisingly, moreover, it is shown that the chloral which has to be
removed with great effort is formed in a considerably smaller amount.
Benzotrichloride can--as described in U.S. Pat. No. 4,851,597 be added to
the prepurified EDC (feed EDC).
The invention is described in more detail in the example below. Percentage
figures relate in this to the weight.
EXAMPLE
An apparatus is used comprising a reservoir for EDC, a metering pump, an
evaporator tube, packed with glass beads, connected to this and which
again is connected to a quartz tube which has an internal diameter of 18
mm and can be heated over a length of 500 mm. The outlet of the quartz
tube is connected to three washing flasks, connected in sequence, and a
gas collection flask. The first washing flask seen from the end of the
quartz tube is furnished with a cooling jacket (water cooling) and serves
to condense the unreacted EDC. The second and third washing flasks contain
distilled water for trapping the hydrogen chloride resulting from the EDC
cleavage. The reaction gases now free of HCl and only containing traces of
EDC (VC +by-products) finally pass through a gas collection flask for
sampling.
During each experiment, the evaporator tube is heated to 220.degree. C. and
the quartz tube to 490.degree. C. (measured at the internal wall of the
tube at the end of the heating zone). The reservoir is filled with EDC to
which the desired quantity of benzotrichloride has been added. 90 g of EDC
per hour run via the metering pump into the heated evaporator tube and are
evaporated there. The vapors are passed through the quartz tube (residence
time about 10 seconds) and the following washing flasks and the gas
collection flask. After steady-state experimental conditions are
established, the duration of each experiment is 2 hours. The unreacted
dichloroethane condensed out in the first washing flask is then weighed,
analyzed for by-products by GC and the hydrogen chloride contained in the
EDC is separated off by washing with water. The aqueous phase is combined
with the washing waters from the second and third washing flasks and the
hydrochloric acid is titrated. This gives the EDC conversion in the quartz
tube. The gas sample contained in the gas collection flask is analyzed by
GC for VC and by-products.
TABLE
______________________________________
Addition of benzotrichloride to EDC (feed quality)
Chloral content
Amount (ppm) Conversion (%)
(mg/100 g of EDC)
______________________________________
0 51.8 0.4
250 75.9 0.1
500 81.1 not detectable
1000 85.1 0.3
______________________________________
The conversion values are averages from at least two determinations.
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